Container forming apparatus

ABSTRACT

A process and an apparatus for blow molding completely finished hollow plastic containers of biaxially oriented material and having a finished neck. A dual-diameter blow pin is positioned between separable mold sections and is movable along its longitudinal axis. A crammer sleeve is reciprocably disposed about the blow pin, and gripping jaws are positioned to close around the blow pin. One end of a heated tubular parison is positioned over a larger-diameter portion of the blow pin, and the parison is longitudinally stretched, axially orienting the material and causing the parison to neck down onto a smaller-diameter portion of the blow pin. The mold sections are closed over the stretched parison, the blow pin is longitudinally inserted to size the inside diameter of the neck opening, the crammer sleeve is inserted to cram axially-oriented material into the neck finishing cavity of the mold and to finish form the neck opening, and the tail surplus material is severed. Upon separation of the mold sections, the crammer sleeve and blow pin are retracted, with the withdrawal of the crammer sleeve removing the severed neck surplus material. The neck forming portions of the mold sections are designed for easy insertion of the blow pin and the provision of a controlled volume of oriented material for the crammer sleeve.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to blow molding, and is moreparticularly directed to the blow molding of completely finished,biaxially oriented hollow containers.

2. Description of the Prior Art

It is known in the prior art that the biaxial blow molding of hollowcontainers, such as bottles, from synthetic resins results in an articleof improved physical properties, such as strength and transparency.Generally, in this blow molding technique, a cooled tubular preform orparison is heated to a suitable orientation temperature, stretched alongits longitudinal direction to axially orient the material and then blownwithin a mold cavity.

In the blow molding of hollow containers, one particularly difficultproblem is to produce large containers with standard-size neck andthread areas. In this situation, the cross-sectional area of thematerial in the neck is greater than in the remainder of the blowncontainer. Accordingly, if a small parison is used to provide asmall-diameter neck and threaded area, the walls of the remainder of theparison will be thinned unduly upon expansion during the blow moldingprocess and detrimentally affect the strength of the container.Conversely, if a parison is used which has sufficient material to formwalls of a relatively large container, the diameter of the neck andthread area will be too large, resulting in additional material beingused unnecessarily in the formation of the container and possiblyproducing flash upon closure of the mold which would require additionalprocessing to finish the container and thus add to the cost ofproduction.

Certain physical characteristics of a container molded of biaxiallyoriented material, such as strength and clarity, are related to theaxial draw ratio possible with a given parison size. The axial drawratio is determined by the unstretched length of the parison and thelength after stretching. These lengths are determined by the desiredcontainer size and weight which, in conjunction with the need to providea standard-size neck and thread portion, define the parison size. Thus,there are techniques in the prior art for blow molding biaxiallyoriented containers in which the achievable axial draw ratios arelimited and the maximum size of the containers which can be formed isrestricted.

Biaxially oriented containers have been made by clamping a portion ofthe parison within neck-forming cavities before stretching of theparison. Techniques are also known in which preforms with finished neckportions molded in a first, preform molding procedure are then stretchedand blow molded. The resulting containers have oriented material in thebody, but the finished neck does not have oriented material. The neckregion, therefore, lacks the clarity and strength that is partiallyobtainable in a container having at least axially-oriented material. Toovercome this problem, processes have been developed which provideorientation of the material in the container neck region. Examples ofsuch processes are disclosed in U.S. Pat. No. 3,651,186, issued to J. N.Hall and U.S. Pat. Nos. 4,065,355 and 4,116,607, issued to R. W.LeGrand. In U.S. Pat. No. 4,108,937, issued to Martineu et al., acylindrical preform is stretched prior to blow molding of the container,resulting in orientation of the material in the neck region, and thematerial in this region is heated to a higher temperature to permitgreater deformation. However, unlike the LeGrand process, the Martineuet al. process does not provide for the formation of closure attachmentmeans on the neck surface such as threads nor is there a precisecalibration of the neck opening inside diameter. Instead, in Martineu etal. the molded container is removed and a separate finishing operationis required to cut the upper portion of the container to produce thefinal form of the finished container.

In the LeGrand patents, a technique is disclosed for parison stretchingand container neck forming in which oriented material is forced by acrammer sleeve into the thread forming area of the mold. The outsidediameter of the crammer sleeve is substantially the same size as theoutside diameter of the finished neck as measured at the base of thethreads, and the outer diameter of the blow pin establishes the diameterof the opening in the finished neck. Since the parison must fit over thecrammer sleeve, the inside diameter of the parison is accordingly fixed.This size constraint and the requirement of a standard-size neck fixesthe ratio of the inside-to-outside diameters of the parison. The necksize is a critical factor since the parison's outside diameter in thecontainer neck region, after stretching, must fit within the openingprovided by the mold neck inserts to prevent flash formation. With theparison diameters thus fixed and the desired container's size and weightparameters determining the length of the parison, the axial draw ratioachieveable is also fixed for a given size container, mandrel and neckthread mold inserts. This technique, therefore, limits the flexibilityin selection of the axial draw ratio.

A related problem in the prior art technique of forming containers ofbiaxially oriented material having finished necks is the provision of anadequate quantity of oriented material to form closure attachment meanssuch as threads. Thus, in a technique such as disclosed in the aforesaidLeGrand patents in which the parison is axially stretched onto acalibrating blow pin and the mold sections closed to size the outerdiameter of the container neck, there may be insufficientaxially-oriented material available below the crammer sleeve to providewell-defined shapes for all the threads. Merely increasing the traveldistance of the crammer to increase the amount of material disposedbelow the crammer is not a completely satisfactory solution since thecrammer would then be required to pass through a larger quantity ofaxially-oriented material, which may adversely affect the capability ofthe crammer to form a smooth, cleanly-severed neck end surface. Anexcessive amount of oriented material below the crammer may alsoadversely affect the distribution of the material along the length ofthe container neck such that the threads and the lower end of the neckare improperly formed.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aprocess and apparatus for blow molding containers of biaxially orientedmaterial.

Another object of the invention is to provide a process and apparatus ofthe foregoing type for blow molding containers having oriented materialin the body and in the neck portions.

Another object of the invention is to provide a process and apparatus ofthe foregoing type for blow molding a completely finished containerwithin the mold.

A further object of the present invention is to provide a process andapparatus of the foregoing type for blow molding oriented containersfrom tubular preforms or parisons.

Yet, a further object of the invention is to provide a process andapparatus of the foregoing type which provides greater flexibility inthe selection of the axial draw ratio of the tubular parison from whichthe container is molded, thereby permitting greater control of theproperties of the blown container.

Still a further object of the invention is to provide a process andapparatus of the foregoing type in which a controlled quantity ofaxially oriented material is provided to form well-defined closureattachment elements on the container neck.

These and other objects of the present invention are achieved in a blowmolding process and apparatus having a dual-diameter blow pin with alarger-diameter calibrating portion equal to the inner diameter of thefinished neck opening and a smaller-diameter portion on the leading end.A crammer sleeve is reciprocally disposed about the blow pin and agripping clamp is positioned to close around the blow pin. A heatedtubular parison is placed onto the larger-diameter portion of the blowpin and is clamped thereon by the gripping clamp. The parison isstretched, causing it to neck down to a first thickness on thesmaller-diameter portion of the blow pin which establishes a quantity ofmaterial available for forming the container neck, and forming a yetthinner-walled portion at the end of the pin which ultimately forms thebody of the blown container. The mold sections are closed, the parisonis blown, the blow pin is longitudinally inserted to calibrate or sizethe neck's inner opening, and the crammer sleeve is advanced to pushadditional oriented material to finish form the neck and to seversurplus material to form a finished neck opening. The neck forming areasof the mold sections are configured in the region where the neck surplusmaterial is severed to provide a controlled amount of oriented materialwhich is crammed to form the neck.

BRIEF DESCRIPTION OF THE DRAWINGS

The above description, as well as further objects, features andadvantages of the present invention, will be more fully appreciated byreference to the following description of a presently-preferred butnonetheless illustrative embodiment in accordance with the invention,and the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a portion of the apparatus of thepresent invention;

FIG. 2 is a view similar to FIG. 1, wherein the parison has beenlongitudinally stretched and the mold sections have closed thereon;

FIG. 3 is a view as in FIG. 2, wherein the blow pin has beenlongitudinally inserted to calibrate the neck opening;

FIG. 4 is a view as in FIG. 3, wherein the crammer sleeve has beenlongitudinally inserted;

FIGS. 5 and 6 are views as in FIG. 4, showing different stages in theseparation of the mold sections and retraction of the blow pin andcrammer sleeve; and

FIG. 7 is a view as in FIG. 5, wherein the blow pin and crammer sleevehave been fully retracted and the molded container is being removed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 of the drawings, a tubular preform or parison 10has an end portion positioned over a blow pin or mandrel, designatedgenerally as 12, and is held thereon between the jaws of a gripper clamp14. The parison 10, a length of tubular, orientable material, has beenheated to a suitable orientation temperature. The blow pin 12 has alarger-diameter portion 16 connected to a smaller-diameter end portion18 by a tapered, intermediate portion 20. Extending along thelongitudinal axis of the blow pin 12 is a central passage or conduit 22through which pressurized fluid is introduced in a known manner to blowmold a container within a mold cavity in a known fashion. The blow pin12 is connected to a conventional mechanism (not shown) which moves theblow pin up and down along its longitudinal axis.

A tubular crammer sleeve 24 is disposed coaxially about an upper portionof the blow pin 12 and, as shown, contacts the upper end surface of theparison 10. Adjacent to the free end of the crammer sleeve 24 is acircumferential recess or notch 26, the purpose of which will bedescribed more fully below. The crammer sleeve 24 is connected to aconventional actuating mechanism (not shown) which moves the sleeve upand down over the blow pin 12, independently of the blow pin.

Positioned above the upper surface of the gripper clamp 14 and the upperend surface of the parison 10 is a stripper plate 28 with an aperture 30through which the blow pin 12 and crammer sleeve 24 freely pass. Thestripper plate 28 is stationarily supported to assist in the removal ofthe top surplus material from the crammer sleeve 24, as will bedescribed more fully below.

Referring now to FIG. 2 of the drawings, the lower end portion of theparison 10 has been grasped by a clamp 32 and stretched longitudinally,thus axially orienting the parison material. By way of illustration, theclamp 32 may conveniently be used to place the parison onto the blow pin12, and during its withdrawal effect the stretching of the parison. Sucha technique is disclosed in the applicants' co-pending application Ser.No. 169,141, filed July 15, 1980. During the stretching, the parisonnecks down in the container neck area 34 and stops at a first wallthickness when its inside surface reaches the surface of thesmaller-diameter portion 18 of the blow pin 12. This first wallthickness provides a quantity of material used in the formation of thefinished container neck. The parison necking process continues below theend of the blow pin 12, to a second, thinner wall thickness portion 36which will be blown to form the body of container. Mold sections 38 of aseparable mold have been closed upon the stretched parison byconventional means (not shown). Each mold section 38 has a cavity 40which defines the contours of the container and a neck forming insert 42disposed above the cavity. The neck forming insert 42 has a cylindricalsurface 44 provided with a number of recessed, concave grooves 46. Thecylindrical surface 44 forms the outside surface of the finishedcontainer neck and the grooves 46 form the threads on the outer surfaceof the neck. While thread-forming grooves are shown, it would also bepossible to form other types of projections for attachment of acontainer closure, such as lugs or the like. The outside diameter of theblow pin portion 16 is substantially the same as the inside diameter ofthe finished container neck opening and the outside diameter of thecrammer sleeve 24 is substantially the same as the outside diameter ofthe finished container neck at the base of the neck threads or similarattachment means. The diameter of the blow pin portion 18 is sized suchthat when the parison 10 is stretched the thickness of the stretchedmaterial in this region provides a controlled or determined quantity ofaxially-oriented material which is used in the formation of the finishedcontainer neck. By proper sizing of the diameter of blow pin portion 18,the amount of material available can be controlled when the parison 10is blown into contact with the neck forming inserts 42, to that requiredto obtain the desired container neck inner and outer diameters.Subsequently, oriented material provided by the crammer sleeve 24 isthen only needed to form the closure threads, as will be described morefully below.

Above the thread-forming grooves 46, in the region of the finished, openend of the container neck, the neck forming inserts 42 are provided witha recessed region or reservoir 47 which is defined, for illustrationpurposes, by a cylindrical sidewall 48 connected at its lower end by aninclined surface 50 to the cylindrical surface 44 of the insert 42. Thecylindrical sidewall 48 has a larger diameter than the cylindricalsurface 44, and the inclined interconnecting surface 50 may be orientedat any suitable angle, such as 30° relative to the vertical direction.The inclined surface 50 may be fabricated of a suitable, hardenedmaterial and cooperate with the crammer sleeve 24 to sever surplusmaterial from the neck region and finish form the open end of thecontainer. The volume afforded by the reservoir 47 provides a controlledamount of axially-oriented material which may be forced by the crammersleeve 24 into the neck forming inserts 42 to form well-defined threadson the container neck, as will be described more fully below.

The foregoing configuration for the reservoir 47 of a cylindrical walland inclined-lower surface is illustrative only. Other appropriateconfigurations for the sidewall and the lower surface may be used aslong as the reservoir provides a controlled volume of axially orientedmaterial which is available to be forced by the crammer into the neckforming inserts.

As shown in FIG. 2, the upper portion of each neck forming insert 42 hasanother recessed region 52 of generally truncated shape which, forexample, may have a conical surface 54 extending above the cylindricalsidewall 48 and merging into a straight, cylindral zone 56. The recessedregion 52 provides a receiving space in the insert 42 for the parisonmaterial displaced by movement of the blow pin 12 and crammer sleeve 24,thus removing the material from the movement path and providing foreasier passage of the blow pin and the crammer sleeve. Additionally,after the mold sections 38 have closed and the gripper clamps 14 havereleased the parison 10, the recessed region 52 provides space toreceive the upper portion of the parison pushed therein by movement ofthe crammer sleeve 24.

The operation of the blow molding apparatus can be discerned byreference to the drawings. The parison 10 is placed upon thelarger-diameter portion 16 of the blow pin 12 by a suitable means, suchas the clamp 32 which has grasped the lower end portion of the parison(FIGS. 1 and 2). The tapered portion 20 of the blow pin 12 serves toguide and center the parison 10 onto the blow pin, and the end of thecrammer sleeve 24 serves as a stop to correctly position the parisonrelative to the gripper clamps 14. The gripper clamps 14 are then closedupon the parison 10, securely holding the parison onto the blow pin 12,and the clamp 32 longitudinally stretches the parison into theconfiguration shown in FIG. 2 as it withdraws from the mold. Subsequentto the longitudinal stretching of the parison 10, or concurrentlytherewith, the mold sections 38 are closed onto the parison. As can beseen from FIG. 2, the smaller-diameter portion 18 of the blow pin 12 issized so that the stretched parison, after it has necked down onto thisportion of the blow pin, has an outer diameter less than the final outerdiameter of the finished container neck as defined by the cylindricalsurface 44 of the neck forming inserts 42. This provides a spacesurrounding the parison to prevent formation of a flash when the moldsections are closed.

As shown in FIG. 3, after the parison 10 has been longitudinallystretched and mold closure has commenced, pressurized fluid isintroduced through the blow pin central passage 22, forcing the parisonagainst the contoured surfaces of the neck forming inserts 42 andcausing the lower portion 36 of the stretched parison to begin to assumethe shape of the mold cavity 40. More particularly, the parison 10 isdisplaced against the recessed region 52, to form a bulbous or bubblelike configuration, and against the cylindrical surface 44. The blow pin12 is longitudinally inserted through the parison 10 to further forcethe neck portion of the parison into conformity with the cylindricalsurface 44 of the neck forming inserts 42 and simultaneously to size orcalibrate the inside diameter of the container neck opening.Displacement of the parison against the inserts 42 by the pressurizedfluid permits easier passage of the blow pin 12.

The crammer sleeve 24 is inserted longitudinally into the parison 10,forcing oriented material contained within the reservoir 47 into thethread-forming grooves 46 to finish form well-defined threads on theexterior surface of the container neck (FIG. 4). When the crammer sleeve24 is fully advanced, as shown in FIG. 4, the lower end surface of thesleeve abutts the inclined lower surface 50 of the reservoir 47 to seversurplus material 58 from the neck and to provide a finished end surfacefor the open end of the neck. It can also be seen that the stillmalleable condition of the parison material in the region around thelower end portion of the crammer sleeve 24 causes some of the materialto be forced into the circumferential groove 26 adjacent to the end ofthe crammer sleeve where the material attaches until subsequentlyremoved.

FIG. 4 illustrates another advantageous feature of the recessed region52 in the inserts 42 and the parison material bubble formed by thepressurized fluid. As the crammer sleeve 24 is advanced, there is atendency for the parison material to cling to the sleeve and move alongwith it. The interior volume of the bubble provides a space into whichthis material can be displaced, thus removing an obstruction to thesleeve movement and eliminating a possible adverse effect upon theamount of axially oriented material which is crammed into the containerneck.

While not specifically shown in the drawings, the gripper clamps 14 maybe retracted after the mold sections 38 have closed onto the stretchedparison. Retraction of the gripper clamps 14 facilitates passage of theblow pin 12 and crammer sleeve 24 through the parison 10. As notedabove, movement of the upper end portion of the parison 10 caused byoperation of the blow pin 12 and crammer sleeve 24 subsequent to theretraction of the gripper clamps 14 is accommodated by the recessedregion 52 so that the parison material does not hinder passage of thecrammer sleeve.

After the container has been blown for an appropriate time, the crammersleeve 24 is retracted to separate the severed surplus material 58 fromthe finished container, the mold sections 38 are separated, and the blowpin 12 is retracted. As shown in FIGS. 5, 6 and 7, retraction of thecrammer sleeve 24 lifts the severed surplus material 58 from the end ofthe finished neck, and upon separation of the mold sections 38, thecontainer drops by gravity from the mold. During its descent, thefinished container is guided off the blow pin 12 by the lower,smaller-diameter portion 18 of the blow pin. The neck surplus material58 adhering onto the circumferential notch 26 of the crammer sleeve 24can be readily knocked off upon retraction of the crammer sleeve throughthe aperture 30 in the stripper plate 28.

It is contemplated that a control system or similar means would beprovided to regulate movement of the components and the sequence andduration of the operational features of the blow molding apparatus asdescribed above. Thus, the closing of the gripper clamps 14 onto thepositioned parison 10, the stretching of the parison and the closing ofthe mold sections 38 would be appropriately correlated and controlled.Similarly, the steps of inserting the blow pin 12, introducing thepressurized fluid through the passage 22, and inserting the crammersleeve 24 would be properly sequenced and timed. In this regard, whilethe operational sequence described above provides for insertion of theblow pin 12 after the introduction of the pressurized fluid, these twosteps may occur simultaneously. As noted above, introduction of thepressurized fluid just before or simultaneously with blow pin insertionis advantageous since the stretched parison in the container neck regionis distended to permit the blow pin to be inserted more easily.

It is important to note that the timing relationship between the variousoperational sequences described above are critical due to the cooling ofthe parison within the mold cavity. It is, therefore, also within thescope of this invention to cram the oriented material in the neck regionbefore, during, or after blowing of the container body, depending uponthe cooling residence time required for the particular materialutilized, once the container neck opening has been calibrated. It isalso within the scope of this invention to control the blow pintemperature by direct application of heat, by cooling or by use ofinsulated material for the blow pin to prevent the neck material fromcooling during the stretching of the parison and closing of the mold,thereby enhancing the ability of the crammer sleeve to displace thematerial into the neck forming inserts.

This invention is applicable to the formation of any article havingbiaxial molecular orientation and a relatively small neck or thread areacompared with the body portion of the article. The invention isapplicable for the production of these articles from any orientablethermoplastic resin, such as polyolefins, poly(vinyl chlorides),acrylonitrile-butadiene-styrene polymers, styrene-butadiene copolymers,various styrene polymers and copolymers, polyamides, polyvinylidenechloride polyers and copolymers, and the like. Preferred resins includecrystalline polymers such as polymers of at least one mono-1-olefinhaving 2-8 carbon atoms per molecule, and more preferably, polymers andcopolymers of ethylene, propylene, and 1-butene, with polypropylenebeing especially preferred.

Although not particularly illustrated in the drawings, it is understoodthat all the components described above are arranged and supported in anoperative fashion to form a complete and operative system. Further, itis understood that all ancillary components such as actuation means,fluid coupling, control systems and components, etc., have not beenspecifically described, but such components are known in the art andwould be appropriately incorporated into the operative system. Ofcourse, variations of the specific construction and arrangement of theblow molder disclosed above can be made by those skilled in the artwithout departing from the invention as defined in the appended claims.

We claim:
 1. An apparatus for blow molding a finished, hollow, biaxiallyoriented container from a tubular parison of orientable plastic materialheated to a suitable orientation temperature for the material,comprising:a blow pin having a first portion of a first diameter forreceiving an end portion of the parison and a second portion of asmaller diameter; means for introducing a pressurized fluid through theblow pin; gripping means disposed adjacent to and movable towards theblow pin for clamping an end portion of the parison onto said firstportion of the blow pin; a tubular sleeve slidably disposed about theblow pin; means cooperating with the gripping means for longtudinallystretching the parison; separable mold sections disposed to close overthe blow pin, each section having a container forming and neck finishingcavity; and operating means that cause (a) the gripping means to clampan end portion of the parison onto the first portion of the blow pin,(b) the stretching means to stretch the parison along the longitudinalaxis of the parison, axially orienting the parison material and causingthe parison to neck down onto the second, smaller-diameter portion ofthe blow pin, (c) the mold sections to close the container forming andneck finishing cavities about the blow pin and the stretched parison,(d) the introducing means to introduce pressurized fluid into thestretched parison to transversely stretch the parison material and formthe molded container, and (e) the tubular sleeve to be moved along thelongitudinal axis of the blow pin, from a first position above thegripping means, to a second position with the sleeve within the grippingmeans and the neck finishing region of the cavity to cram orientedmaterial into the cavity.
 2. The apparatus as defined in claim 1,including additional means operable to move the blow pin longitudinallyalong the blow pin axis, said means operable to move the blow pin intothe neck finishing region of the cavity to transversely stretch theparison material and calibrate the inside opening of the container neck.3. The apparatus as defined in claim 1, wherein the neck finishingregion of the cavity of each mold section has a recessed portion with asidewall of a larger diameter than the outer diameter of the neck, saidrecessed portion providing a reservoir for a controlled volume oflongitudinally-stretched parison material which is crammed into the neckfinishing cavities by the tubular sleeve.
 4. The apparatus as defined inclaim 3, wherein the recessed portion has an annular surface whichcoacts with the tubular sleeve to sever surplus parison material.
 5. Theapparatus as defined in claim 1, wherein the smaller-diameter portion ofthe blow pin is sized to provide an annular clearance between thestretched parison and the neck finishing region of the cavity of eachmold section with the mold sections closed.
 6. The apparatus as definedin claim 1, wherein the smaller-diameter portion of the blow pin issized to provide a controlled volume of longitudinally-stretched parisonmaterial required to form the container neck.
 7. The apparatus asdefined in claim 3 or 4, wherein the neck finishing region of the cavityof each mold section has a second recessed portion disposed suprajacentto said recessed portion, said second recessed portion providing spaceto receive an end portion of the parison during the blow molding of thecontainer.